Integrated printhead with encoding circuit

ABSTRACT

Ink jet printhead comprising a driving and encoding circuit ( 20 ) having a grid-like structure, including a plurality of inputs ( 24 ), a plurality of selecting elements ( 12 ), a plurality of actuating elements (I1) and at least one identifying element ( 21 ) of said printhead. Each identifying element ( 21 ) is associated with a corresponding selecting element ( 12 ) and corresponds to nodes arranged along a row or column of said grid-like structure, and is scanned, together with said actuating elements ( 11 ), during a preliminary checking step.

TECHNICAL AREA OF THE INVENTION

This invention relates to a thermal type ink jet printhead, in which aplurality of actuating elements are activated selectively by an externalcontrol circuit, to cause the ejection of ink droplets through nozzlesplaced in correspondence with the actuating elements themselves.

In particular, this invention relates to an integrated printhead,comprising in the integrated circuit elements identifying the headitself, in accordance with the description provided in the main claim.

TECHNICAL BACKGROUND

The constitution and general mode of operation of a thermal type ink jetprinthead, and in particular of the type known as “top shooter”, i.e.that emits the ink droplets in a direction perpendicular to theactuating assembly, are already widely known in the art, and, thereforewill is not be described in detail here, while only some characteristicsof relevance for the purposes of the understanding of this inventionwill be described more particularly.

With reference to FIG. 1, an integrated printhead (head) 10, accordingto the known art, is made of an integrated circuit, for instance NMOS orbipolar type and comprises a plurality of nozzles 31, positioned on thehead 10 according to a predefined order and suitable for ejecting ink ona medium, generally of paper, and a plurality of inputs or contacts 23;provided for connecting the head 10 to an external control circuit,suitable for commanding the selective actuation of the various nozzles31.

The known head 10 (FIG. 2) is made of a grid-like driving circuit (M×N)comprising a plurality, M of actuating assemblies 14. Each actuatingassembly 14 in turn comprises a plurality N of selecting-elements ortransistors 12 and an equivalent number of actuating elements orresistors 11 which are provided for causing, in a known way, ejection ofthe ink from the nozzles 31.

Also described by the U.S. Pat. No. 5,363,134 is an integrated printheadthat comprises an encoding circuit, in which, by burning programmablefuses, information can be stored about the general characteristics ofthe head, such as for instance: colour head, its resolution, number ofnozzles.

The encoding circuit is integrated on the same substrate as theselecting and activating circuit of the resistors and is composed of arow of programmable fuses, each of which is connected in series with atransistor.

Besides, each couple comprising a fuse and a transistor of the encodingcircuit, is permanently connected to an Address Line and has theadvantage of permitting reading of the coding stored without increasingthe number of head connections.

It is in fact advantageous to have the possibility of identifying,through the printer's control circuit, a set of head characteristics,stored during the production of the head, that can cause anon-uniformity of operation between the various nozzles, considerablyworsening the print quality.

Some of the characteristics that may be stored are, for instance,misalignments or differences of shape, diameter or centre distancebetween the nozzles.

In possession of this information, the control circuit can compensate,by varying the energy supplied to the resistors, any differences involume of the ink droplets or of speeds which are caused by thesenon-uniformities.

This solution has the disadvantage, however, of adding an encodingcircuit, formed by N couples of fuses and transistors, where N is thenumber of addresses in the grid, to those already existing on the head,with a relative increase in the surface area of the integrated circuitand greater costs and manufacturing difficulties. In addition, theencoding circuit can contain at most N fuses.

SUMMARY OF THE INVENTION

The object of this invention is to produce an encoding of the head byusing free positions of the grid-like circuit of the head, withouthaving to add a new circuit for the encoding.

A second object is that of using circuits already existing in the driverof the head for reading of the encoding, without having to build aspecific circuit, modifying only the software.

A third object is that of producing an encoding of the head using thealready present circuits mentioned above, to which only a line of fusesfor the encoding is added.

A fourth object is to produce an encoding with a number of fuses greaterthan the number of addresses.

These objects are attained by the integrated printhead of the invention,according to the characteristic parts of the main claims.

These and other characteristics of this invention will become clear fromthe following description, provided by way of non-restrictive example,with the aid of the accompanying drawings.

LIST OF FIGURES

FIG. 1 represents a schematic assembly view of an integrated printheadaccording to the known art;

FIG. 2 represents a wiring diagram of the circuit elements of anintegrated printhead according to the known art;

FIG. 3 represents a,block diagram of the control circuit of the headaccording to the invention;

FIG. 4 represents a wiring diagram of the circuit elements of anintegrated head according to the invention;

FIG. 5 represents a wiring diagram of the circuit elements of a secondembodiment of an integrated head according to the invention;

FIG. 6 represents a block diagram of a second embodiment of the controlcircuit of the head according to the invention.

DESCRIPTION First Embodiment

With reference to FIG. 4, an integrated printhead (head), according tothe invention, is made up of an integrated circuit, for example NMOS orbipolar type, and comprises a driving and encoding circuit 20,consisting of a plurality of actuating assemblies 14, of known type, anda plurality of actuating assemblies with encoding or encoding assemblies24.

Each actuating assembly 14, of known type, comprises a plurality ofactuating elements or resistors 11, which are provided for causingejection of the ink droplets from the nozzles 31, and correspondingselecting elements or transistors 12.

In each actuating assembly 14, each transistor 12, of known type, hasits drain terminal connected to one of the two terminals of the resistor11, the source terminal connected in common to the sources of thetransistors 12 belonging to the same actuating assembly 14, and the gateterminal connected to the inputs or contacts 23 corresponding to addressselection lines (Address Line Select or addresses) A_(I=1−N).

The resistors 11 belonging to an actuating assembly 14 have the secondterminal connected in common and to an input or contact 23 correspondingto a primitive feeding line (Primitive Select or primitive) P_(J=1−M).

Each encoding assembly 24 comprises, in addition to the actuatingelements, (resistors) 11 of known type, a plurality of identifyingelements (resistors or fuses) 21, placed in correspondence with thenozzles of the grid not used for printing, and also comprises aplurality of selecting elements (transistors) 12, in correspondence withthe resistors or fuses 21 and the resistors 11.

The identifying elements 21 are therefore in correspondence with emptyis positions of the grid (M×N).

In each encoding assembly 24, each transistor 12, of known type, has thedrain terminal that can be connected to one of the two terminals of theresistor 11 or of the fuse 21, the source terminal connected in commonto the sources of the transistors 12 belonging to the same encodingassembly 24 and the gate 20 terminal connected to the contacts 23corresponding to address selection lines (Address Line Select oraddresses) A_(I=1−N).

The resistors 11 and the fuses 21 belonging to an encoding assembly 24have the second terminal connected in common and to a contact 23corresponding to a primitive feeding line (Primitive Select orprimitive) P_(J=1−M).

In particular, each actuating assembly 14 and each encoding assembly 24are activated by means of contacts or primitives P_(J=1+M) and eachtransistor 12 is selected by means of contacts or addresses A_(I=1+N).

The head according to the invention therefore comprises a driving andencoding circuit (20) having a grid-like structure, formed by theactuating 11, identifying 21 and selecting 12 elements, having M rowsand N columns in which:

N is the number of Selectable addresses A_(I), and is equal to the sumof the number of resistors 11 and fuses 21; and

M is the number of primitives P_(J) suitable for activation.

Generally, in the known heads, not all the available positions of theM×N grid are used for printing.

For instance, there are polychromatic heads in which the nozzles aredivided into three colour groups, separated by gaps. The nozzles, ofeach group are used for printing with ink of one of the three basiccolours, and the gap is greater than the centre distance between twonozzles. The nozzles located in the gaps are not therefore used forprinting, and the positions of the M×N grid corresponding to thesenozzles are therefore free. In the head according to the invention, thecircuitry part which is usually occupied by the resistors 11, placed incorrespondence with the unused nozzles, may therefore be used toaccommodate the identifying elements or fuses 21, that form the encodingcircuit.

The fuses 21 are burnt, for instance at the time of production of thehead, to store the desired characteristics.

In this way, a circuit is obtained for encoding of the head, usingpositions of the grid that would otherwise be unused, without adding anycircuits and without using any extra area.

Take for example a colour printhead according to the invention,comprising 192 nozzles (31) and having 16 (M) primitives P_(J=1−M) and13 (N) addresses A_(I=1+N) suitable for use.

This gives 208 (16*13=208) positions available for driving the nozzles,of which only 192 are actually used.

Therefore 16 (208−192=16) positions remain free, and these are used, inaccordance with a characteristic element of this invention, toaccommodate, instead of resistors 11, the fuses 21 that form theencoding circuit.

As is known, the actuating elements 11I and selecting elements 12 areselected and commanded by a control circuit 40, external to the head,which comprises a “controller” 41, and a “head driver” 42, and isconnected to the head by means of flexible circuits 44 (FIG. 3).

The controller 41 sends, through buses 43, the signals containing theprint code (DATA), decoding of the 4-bit addresses A_(I=1+N) (CODE) andthe: timings (CONTROL LINE) of the nozzles to be selected, to the headdriver 42, which in

turn converts them into current pulses suitable for activating ejectionof the ink from the corresponding nozzles.

The control circuit 40 is connected to the head by means of flexiblecircuits 44 and in particular by means of the contacts P_(J=1+M) andA_(I=1+N) (FIG. 3).

In the known heads, the control circuit 40 activates the ejection of inkby the nozles of the head, according to the following order:

activates for a given time, a first address A_(I);

electrically powers with predetermined current pulses and through thecontacts P_(J), a predefined configuration of primitives;

activates in sequence a second address;

electrically powers, with predetermined current pulses and through thecontacts P_(J), a second predefined configuration of primitives; and soon in successive steps until activation of the N addresses is complete.

Through logic signals and in a known way the control circuit 40 of theprinter, therefore, is suitable for activating in sequence the addressesA_(1−N) and, consequently, the N gates of the transistors 12 of theactuating assemblies 14 and of the encoding assemblies 24.

By means of the contacts P_(J), the control circuit is suitable, in aknown way, for electrically powering, upon variation of the addressesA_(I), predefined configurations of primitives so as to activate theejection of ink by the nozzles corresponding to the active address A_(I)and to the configuration of primitives powered.

In the head according to the invention the encoding of the head isphysically produced by activating, through the contacts A_(I), theaddresses corresponding to the fuses 21 that have to be burnt, and bypowering the corresponding primitives with pulses having a voltage and aduration suitable for burning the fuses (for example, voltage of 10 Vand pulses of 3÷4 μs).

In this way, codes can be stored on each head corresponding to datarelating to characteristics of the head, such as for instance dropletdiameter and speed, threshold energy.

The maximum pulse voltage +V applied to the contacts P_(J) in theencoding step must be less than, with a safety margin, the breakdownvoltage (drain/substrate) of all the selecting elements 12 (MOS)connected to P_(J) to avoid damaging the head. For instance, in headswith droplets of a few pl,

where the threshold energy is 1-2 μJ, the currents are less than 100 mAand the voltage applied in the encoding step is approx. 5-6 V, while thebreakdown voltage of the transistors is approx. 15 V. In this way, thereis a delta V of safety between the voltage needed to blow the fuses 21and the breakdown voltage of the transistors 12.

According to a characteristic of this invention, to read the encoding, aknown type of circuit called “nozzle check”, which is part of the headdriver 42, may be used without having to build a specific circuit ormodify the driver, using the known control circuit 40, simply bymodifying the head management software.

At the start of each printing step, before activating the ejection ofink, the control circuit 40 checks integrity of the resistors, by meansof the function called “nozzles check” incorporated in the head driver42.

During the nozzle check, the entire grid is scanned by sending to theprimitives P_(J) a current called “check current” to verify integrity ofthe resistors.

The check current is very low (10 mA) and is not sufficient to activatethe ejection of ink by the nozzles, but simply verifies efficiency ofthe resistors.

At the same time, through the check current, the fuses 21 can be checkedto see whether they are open or integral, and thus the encoding storedin the head is read.

Second Embodiment

The second embodiment refers to the case of heads that have the grid(M×N) full, i.e. that use all the M×N nozzles 31, activated by thecorresponding resistors 11.

A printhead according to the invention comprises a driving and encodingcircuit 20 a, a grid, made up of a plurality of actuating assemblies 14,of known type, to which are added one or more addresses A_(I=N+K), afuse 21 and a corresponding transistor 12 are also made, connected toeach of the addresses A_(I=N+K) added to the grid circuit (FIG. 5).

Take by way of example a head comprising 208 nozzles 31 and having 16(M) primitives P_(J=1-M) and 13 (N) addresses A_(I=1+N) suitable foruse.

There are therefore 208 (16*13=208) positions available for driving thenozzles, all occupied by the resistors 11, and no free position remainsto be used for the encoding circuit, that could accommodate the fuses21.

In this case, unable to make use of empty positions of the grid M×N toaccommodate the encoding circuit, one or more addresses A_(I=N+K) areadded to the grid circuit, to which a fuse 21 and a correspondingtransistor 12 are connected.

In the example cited, of a head with 16 (M) primitives P_(J=1−M) and 13(N) addresses A_(I=1+N), for each address A_(I=N+K) added, there are 16(M) positions available for accommodating a fuse 21 and a transistor 12,and therefore 16 encoding bits available for each new address.

The encoding circuits (fuses 21 and transistors 12) cannot be includedin the grid, and are therefore placed in the area available between thecontacts 23.

In the second embodiment also, reading of the encoding takes place inthe nozzle check phase; in this case, in the nozzle check the driver 42scans all the N×M positions occupied by the resistors 11 activating thenozzles, and K connections 44 more are needed between the controller 41and the addresses A_(I=N+K) added for the encoding, as depicted in FIG.6.

The K addresses added are therefore only activated in the step ofreading the encoding and in that of physically producing the encoding,which takes place in the same way as described in the first embodiment.

The printhead, according to the invention, offers numerous advantages incomparison with the known art. In fact, the encoding circuit uses partsof the existing driving circuit and contacts, without changing them orwith a limited increase in the surface area occupied by this circuit.Furthermore, for reading of the encoding of the head, the nozzle checkstep already present in operation of the head is used, without slowingdown the printing preliminaries.

Naturally, without prejudice to the principle of the invention, theembodiments and construction details may be amply varied with respect towhat has been described and illustrated purely by, way ofnon-restrictive example, without departing from the scope of thisinvention.

1. An ink jet printhead comprising: a driving and encoding circuithaving a grid-like structure including a plurality of inputs and aplurality of selecting elements, a plurality of actuating elementsassociated with said driving and encoding circuits, and suitable forbeing selectively addressed and commanded by said selecting elements inresponse to at least one command signal received through said pluralityof inputs, so as to cause the ejection of ink droplets from said ink jetprinthead, and at least one identifying element of said ink jetprinthead, wherein each of said identifying elements of said ink jetprinthead is associated with a corresponding selecting element of saiddriving and encoding circuit, to be selectively addressed and identifiedin response to at least one corresponding identifying signal receivedthrough said plurality of inputs.
 2. The ink jet printhead according toclaim 1, wherein said plurality of actuating elements and each of saididentifying elements are suitable for being sounded through at least onecorresponding command signal received through said plurality of inputs,during a preliminary checking step, the purpose of which is to identifysaid ink jet printhead and to confirm the correct operation of saidactuating elements.
 3. The ink jet printhead according to claim 1,wherein said actuating elements are resistors and said ink jet printheadis of the thermal, bubble type for activating the ejection of said inkdroplets.
 4. The ink jet printhead according to claim 1, wherein saididentifying elements are made of a plurality of resistors each resistorhaving a resistivity that has been selectively set during amanufacturing process of said ink jet printhead, depending on itscharacteristics.
 5. The ink jet printhead according to claim 1, whereinsaid identifying elements occupy positions of the grid-like structurethat are located in correspondence with nozzles not used for printing.6. An ink jet printhead comprising: a driving and encoding circuithaving a grid-like structure and including a plurality of inputs, aplurality of selecting elements, an plurality of actuating elementssuitable for being selectively addressed and commanded by said selectingelements in response to at least one command signal received throughsaid plurality of inputs, so as to cause the ejection of ink dropletsfrom said ink jet printhead, and at least one identifying element ofsaid ink jet printhead, wherein each of said identifying elements ofsaid ink jet printhead is associated with a corresponding selectingelement of said driving and encoding circuit, for being selectivelyaddressed and identified in response to at least one correspondingidentifying signal received through said plurality of inputs.
 7. Anintegrated ink jet printhead comprising: a plurality of actuatingelements for causing ejection of ink droplets from said ink jetprinthead, a driving and encoding circuit, having a grid-like structure,for selectively addressing and commanding each of said actuatingelements, said grid-like structure being organized into rows and columnsthat define a plurality of nodes corresponding to said actuatingelements, and one or more identifying elements of said ink jetprinthead, wherein said one or more identifying elements of said ink jetprinthead correspond to nodes arranged, along a given row or column ofsaid grid-like structure, and further wherein said one or moreidentifying elements are also provided for being scanned, together withsaid actuating elements, during a preliminary checking step, thepurposes of which are both to identify said ink jet printhead and toconfirm correct operation of said actuating elements.